One process for regulating the thickness of extruded flat sheets or plates of thermoplastic has been disclosed by DE 31 07 701 C2, for instance. In this process, measurement values are found during continuous measurement of the thickness of the flat sheet or plate using a thickness gauge transversely to the draw-off direction; these values are averaged, and control is carried out as a function of the ascertained deviation between the actual values and a specified command value.
This is a classical process of readjustment as a function of the ascertained differential signals between actual and command variables.
A similar method has also been disclosed by EP 0 203 479 A2. Once again, a specific mean value is formed via measurement value pickups, a command value is fixed, and after the deviation of the actual value from the command value has been found, the control device is altered to make a correction.
Although partial improvements are attainable with such processes and devices, it has nevertheless been found that particularly in a closed-loop control process that is dependent on a number of control parameters, the fastest possible optimization and subsequent stabilization of the attained optimal control can be achieved only with difficulty, particularly if the variation in the deviation is to be as slight as possible.